We have expressed envelope glycoprotein from pig endogenous retrovirus PERV. Genes coding for this protein were cloned into vaccinia virus and expressed by infecting CV-1 cells. The glycoprotein was purified by affinity chromatography and detected by PAGE gels and western blots. This material will be used to coat ELISA plates and test for antibodies to pig retrovirus. As a control, abbits immunized with PERV env peptides will be used. Test sera will include humans who were exposed to pig plasma proteins, such as clotting factors, or to pig cells, as by transplantation of porcine islet cells. We will also test monkey sera from experimental pig-to-monkey transplantation studies, including animals tolerized with pig bone marrow. Since recent studies have shown that pig endogenous retrovirus can grow in human cells, we are looking for anti-PERV antibodies as a sensitive probe of spread from pig organs to human recipients. On the other hand, if we can rule out human infection by PERV, the data might provide an upper limit on the risks associated with transplantation of pig organs.